Abstract
In this paper, the hybridization of standard particle swarm optimisation (PSO) with the analytical method ( rule) is proposed, which is called as analytical hybrid PSO (AHPSO) algorithm used for the optimal siting and sizing of distribution generation. The proposed AHPSO algorithm is implemented to cater for uniformly distributed, increasingly distributed, centrally distributed, and randomly distributed loads in conventional power systems. To demonstrate the effectiveness of the proposed algorithm, the convergence speed and optimization performances of standard PSO and the proposed AHPSO algorithms are compared for two cases. In the first case, the performances of both the algorithms are compared for four different load distributions via an IEEE 10-bus system. In the second case, the performances of both the algorithms are compared for IEEE 10-bus, IEEE 33-bus, IEEE 69-bus systems, and a real distribution system of Korea. Simulation results show that the proposed AHPSO algorithm converges significantly faster than the standard PSO. The results of the proposed algorithm are compared with those of an analytical algorithm, and the results of them are similar.
THE conventional power grids are radial in nature, and the generation units are typically far away from the loads. In this way, it is inevitable that power will be lost during the transmission and distribution of power to the end consumers. To mitigate these losses, a variety of solutions have been proposed. One possibility is to use superconductor materials for transmission and distribution lines. However, superconductor technology is prohibitively with high cost. Another option is to install power generation units near the consumers. However, due to environmental pollution and social issues, it is not applicable in most of scenarios. Therefore, more recently, the concept of distributed generation has emerged which reduces line losses and is now technologically viable, environment-friendly, and economical.
Due to the advancements in communication technologies, an optimal allocation of distributed generators (DGs) in smart grids would impact many important parameters of the grid including power/energy losses, voltage profile, power quality, reliability, control and stability. As a result, various heuristic methods have been proposed for optimal siting and sizing of DGs in distribution systems [
In addition to optimizing siting and sizing, PSO was utilized to improve a wide range of technical challenges such as the voltage profile, line loading, active and reactive power losses of the power grid in [
The other heuristic approach for the siting and sizing of DGs includes genetic algorithms (GAs) [
A critical challenge with the standard heuristic methods is to overcome the local trapping issue. Due to the increasing usage of PSO for optimal siting and sizing of DGs, this paper uses PSO to evaluate the feasibility of the proposed algorithm. With the limitations of PSO, a hybrid standard PSO and the analytical method ( rule) for siting and sizing of DGs is proposed to reduce the power loss and improve the voltage profile. It is well known that the standard rule is only valid for uniformly distributed loads. However, most of the real loads in power systems are not uniformly distributed. Therefore, in this paper, the standard rule is modified and different rules are devised for specific pattern loads, i.e., uniformly distributed, increasingly distributed, and centrally distributed loads. The rule is extended to randomly distributed loads by placing DG at the bus with of the total load, starting from the source side. Initially, a bus number is determined by using the modified rule. Then, the upper and lower bounds are determined for the search space of the proposed analytical hybrid PSO (AHPSO) algorithm. Thus, instead of searching in the whole area, the search space is limited by using the AHPSO algorithm. Consequently, a fast convergence is achieved without compromising on the siting and sizing aspects from the standard PSO. To demonstrate the effectiveness of the proposed algorithm, different load patterns, i.e., uniformly distributed, increasingly distributed, centrally distributed, and randomly distributed, should be implemented in an IEEE 10-bus system. Then, the performance of the proposed AHPSO algorithm is evaluated for different power systems including a real distribution system of Korea Electric Power Corporation (KEPCO), Korea. The results of the proposed algorithm are compared with those of analytical algorithms. And the results of the proposed AHPSO algorithm are similar to those of analytical algorithms.
The main goal of the proposed algorithm is to minimize the active power loss and improve the voltage profile of the power system. The active power loss [
(1) |
where is the total distance of the feeder; are the sensitivity factors of exact loss formula; are the numbers of buses; are the active power at buses and , respectively; are the reactive power at buses and , respectively; is the reactance of line connecting buses i and j; are the voltage magnitudes at buses i and j, respectively; and are the phase angles at buses i and j, respectively.
(2) |
(3) |
where , are the active and reactive power injected by DG units at bus , respectively; and , are the active and reactive loads at bus , respectively.
The PSO algorithm is a non-linear optimization algorithm [
(4) |
where is the velocity of particle at iteration ; is the position of particle at iteration ; , are the cognitive factor and social factor , respectively; are the random numbers between ; and , are the personal best and globle best among all in the group at iteration , respectively.
The current position can be calculated by adding the current velocity in the previous position.
(5) |
where is the current velocity of particle at iteration .
Reference [

Fig. 1 Swarm cooperation rules. (a) Rule 1. (b) Rule 2. (c) Rule 3.
1) Rule 1: avoid the collision with neighboring birds.
2) Rule 2: match the velocity of neighboring birds.
3) Rule 3: stay near neighboring birds.
Equations (
AHPSO is proposed to overcome the problem of particles being trapped into local minima. The modified rule is combined with the standard PSO, and AHPSO algorithm is developed for the siting and sizing of DGs in the smart grid. The search space for searching the optimal location is reduced by using the modified rule, and then PSO is used to search within the specified bounds. The step-by-step process of the proposed AHPSO algorithm is described as follows:
Step 1: input system data. Total number of iterations, line data (resistance, reactance, and susceptance) and bus data (bus-type, voltage magnitude and angle, active and reactive power limits, etc.) are given.
Step 2: calculate the active power loss. Calculate the active power loss of base case by using exact loss formula and voltage and current by using load flow analysis.
Step 3: site and size DG. Determine the search space by using the modified rule based on the load distribution behavior.
Steps 4 : calculate the total active power loss. For each DG, calculate the total active power loss by (1) if the bus voltage is within the limits. Otherwise, the particle is infeasible.
Step 5: find the and . For each DG, objective function is calculated and compared with . If this value is lower than , set this value as the current and record the corresponding particle position. The smallest active power loss among all is the .
Step 6: update the velocity and position. Update the velocity and position using (4) and (5).
Step 7: terminate criteria. If the conditions below are satisfied, then terminate the loop. Otherwise, set iteration index and go back to Step 4.
The loop termination conditions are: ① no improvement is found; ② the maximum number of iterations is reached. The best siting and sizing represent the minimum real power loss.
The standard rule states that if a DG is placed at two thirds distance from the feeder, the power losses are minimized [
(6) |
where is the total value of power loss at node ; is the total distance of the feeder at time t; is the phasor current density; and is the injected current by DG. The goal of the process is to deploy the DG in a location where the average power loss is minimum. Therefore, it can be expressed as .
1) If the loads are uniformly distributed as shown in

Fig. 2 Different load patterns for IEEE 10-bus system. (a) Uniformly distributed load. (b) Increasingly distributed load. (c) Centrally distributed load. (d) Randomly distributed load.
2) If the load is increasingly distributed as shown in
3) If the loads are centrally distributed as shown in
4) Finally, in the case of random loads, mathematical modeling is not possible. Therefore, the bus is searched, where the load is equal to of the total networks load, starting from the feeder side. This node is considered as the optimal location for the placement of DGs.
5) The real loads of power systems do not exactly follow these specific pattern loads. Therefore, each system load is categorized as based on its proximity to one of four load patterns.
6) An uncertainty gap of is considered for specific pattern, i.e., uniformly distributed, increasingly distributed, and centrally distributed, randomly distributed loads, and is considered for randomly distributed loads.
7) If a node is selected as the optimal node for a given system, the upper and lower bounds of the nodes are selected by using upper node number and lower node number . And will be replaced with 0.1 for specific pattern loads and with 0.2 for random pattern loads. The search space of the proposed PSO will be limited to these upper and lower bounds due to the implementation of the modified rule. Therefore, the search space of the proposed PSO is reduced and the probability of local trapping will also be reduced. Additionally, due to limited search space, the convergence of the proposed PSO will be faster than that of the standard PSO.
The objective of the proposed PSO is to obtain optimal siting and sizing of DGs, minimizing the following objective function as expressed in (7). The first term contains the cost for the deployment of a d-type DG. There are various types of distributed energy sources, which are used as DGs, i.e., gas turbines, stirling engines, diesel generators, steam engines, photovoltaic arrays, and fuel cells. The deployment and maintenance costs for each type of energy source are different. Therefore, the DG-type indicator is defined and used in this paper. The second term contains the penalty cost for voltage limit violation at each bus of the network. If there is a violation, then and the penalty cost will be added. Otherwise, and the whole term will be zero. Therefore, no penalty cost will be added to the objective function. The third term contains the cost for active power loss in the network.
(7) |
(8) |
where are the costs of DG, violation, and power loss, respectively; is the cost for the deployment of a d-type DG; is the voltage at bus i; is the cost of loss at buses i and j; is the power loss at buses i and j; and , are the minimum and maximum voltages at bus , respectively.
The voltage at each bus should not violate and remain in a certain limit, which is specified in (8).
(9) |
The energy balancing of the total network is given by (10), which states that the amount of power injected by the substation and the DG should be balanced with the total load of the network along with network losses.
(10) |
where is the power injected by the substation; and is the power generated by the d-type DG.
The generation bounds of a selected d-type DG units are given by (11). The angle deviation limits at each bus of the network are given by (12). Finally, the current flowing through each line should be within the rated limits as given by (13).
(11) |
(12) |
(13) |
where is the power generated by the d-type; are the minimum and maximum power generated by the d-type DG, respectively; is the angle at node j; are the minimum and maximum allowable angles for voltage at bus j, respectively; is the current at node ; and is the rated current at node .
In order to show the performance of the proposed AHPSO algorithm, three cases are simulated. In the first case, an IEEE 10-bus system is considered and the performance of the modified rule for different load patterns is evaluated. In this case, all the four load patterns, i.e., uniformly distributed, increasingly distributed, centrally distributed, and randomly distributed loads, are considered. In the second case, the convergence speed of the proposed AHPSO for different sizes of networks is evaluated. In addition to IEEE 10-bus, IEEE 33-bus, IEEE 69-bus systems, and a real distribution system in Korea, are also simulated. Finally, we have compared the performance of the proposed AHPSO algorithm with those of an analytical algorithm proposed in [
In the case of the standard PSO, all 10 nodes are in the search space while the search space has been revised by using the proposed AHPSO algorithm. The iteration numbers vs. power loss for all the four load patterns are shown in

Fig. 3 Convergence of standard PSO and AHPSO for different load patterns in IEEE 10-bus system. (a) Uniformly distributed load. (b) Increasingly distributed load. (c) Centrally distributed load. (d) Randomly distributed load.
Due to this reduced search space, the searching speed of the proposed AHPSO algorithm has been increased by 32% for randomly distributed loads and by about 55% for the remaining three load patterns. The improvement has been determined by using the number of iterations taken by each algorithm (standard PSO as reference) for its convergence.
Since the siting and sizing of DGs determined by standard PSO and the proposed AHPSO algorithms are identical, the voltage load profile of the network has been compared before and after placing the DGs, as shown in

Fig. 4 Voltage profile for different load patterns in IEEE 10-bus system before and after placing DGs. (a) Uniformly distributed load. (b) Increasingly distributed load. (c) Centrally distributed load. (d) Randomly distributed load.
It can be observed from
In this sub-section, the performances of the proposed AHPSO algorithm and the standard PSO are compared in different distribution systems. IEEE 10-bus [
The proposed algorithm is firstly tested on IEEE 10-bus, single-feeder, zero-lateral radial distribution system as shown in

Fig. 5 Single-line diagram of IEEE 10-bus system.
IEEE 33-bus system is a radial distribution system consisting 32 branches and 33 buses with total load of 3.715 MW and 2.3 Mvar, and the substation voltage is 12.66 kV as shown in

Fig. 6 Single-line diagram of IEEE 33-bus system.
The IEEE 69-bus system is also a radial distribution system consisting 65 branches, 69 buses, and the total demands of the IEEE 69-bus system are 3802.19 kW and 2694.60 kvar as shown in

Fig. 7 Single-line diagram of IEEE 69-bus system.
The KEPCO distribution system is also a radial distribution system consisting of 4 feeders.

Fig. 8 Single-line diagram of KEPCO distribution system.
The objective is to minimize the active power loss of the network. Therefore, the active power loss after each iteration is shown in

Fig. 9 Convergence of standard PSO and AHPSO for different distribution systems. (a) IEEE 10-bus system. (b) IEEE 33-bus system. (c) IEEE 69-bus system. (d) KEPCO distribution system.
Similar to the previous sections, the siting and sizing of DGs determined by both the standard PSO and AHPSO algorithms are identical for all types of distributions systems, as shown in

Fig. 10 Voltage profiles for different distribution systems before and after placing DGs. (a) IEEE 10-bus system. (b) IEEE 33-bus system. (c) IEEE 69-bus system. (d) KEPCO distribution system.
Before placing the DG, the voltage profiles of some of the buses in all the distribution systems are violating the acceptable bound limits. However, after placing the optimally sized DG at the optimal location determined by AHPSO algorithm, the voltage profile of all the buses in all the systems have moved to the acceptable range.
The performance of the proposed algorithm is compared with that of the analytical algorithm proposed in [
In this paper, a novel AHPSO algorithm has been proposed to determine the optimal siting of DGs in various load distribution patterns including randomly distributed loads. The modified rule is utilized to narrow down the search space of the searching algorithm. Due to the increasing use of PSO for the optimal siting and sizing of DGs in distribution systems, PSO with the modified rule is utilized in this paper. However, the proposed modified rule can be applied to other heuristic algorithms to limit their search space, and finally to avoid local trapping. The convergence speed to the standard PSO and the proposed AHPSO algorithm are compared for two cases. In the first case, the performance is compared for different load distribution patterns in an IEEE 10-bus system. The convergence speed of AHPSO has improved by about 55% for uniformly distributed, increasingly distributed, and centrally distributed loads and by 32% for randomly distributed loads. In the second case, the convergence speed of both the algorithms is compared for different distribution systems. The convergence performance of AHPSO has improved by 32%, 42.59%, 50.91%, and 55.56% for the IEEE 10-bus, IEEE 33-bus, IEEE 69-bus systems, and KEPCO distribution system, respectively. The final result of the siting and sizing of DG is the same in all the cases for both standard PSO and the proposed AHPSO algorithms. In all the cases, the voltage profiles of all the networks have moved to the acceptable range after placing optimally sized DG at the designated position by the proposed algorithm.
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